Rotary cutting dies are used to cut and score sheets of corrugated board to produce a die cut product that can be manipulated into boxes. Rotary cutting dies typically include a curved die board that is configured to mount on a die cylinder. When used, the die cylinder and die board are mounted adjacent an anvil and a nip is defined between the cylinder and the anvil. Sheets of corrugated board are fed into and through the nip and, in the process, the sheet of corrugated board is cut and scored to form the die cut product. Die boards commonly include product and scrap cutting blades, scoring rules, trim and scrap strippers and product ejectors for separating the die cut product from the cutting die.
A common problem with rotary cutting dies that operate on corrugated board is that of controlling the pressure exerted against the corrugated board by the product ejectors. If the pressure is too great, the die cut product is damaged. That is, if the pressure is too great, the flutes are crushed. This makes the resulting boxes weaker and hence the boxes possess less stacking strength and the crushed flutes have a negative impact on the appearance of the product.
On the other hand, if the pressure exerted by the product ejectors is too low, then this will impact the separation of the die cut product from the cutting die during the die cutting operation. That is, if the pressure is insufficient to dislodge or remove the cut die product from the cutting die, it follows that the product will continue with the cutting die and the die cutting operation will be seriously impacted.
It is known to attach product ejectors to the outer surface of the die board. It is also known to seat product ejectors on the bottom of an opening formed in the die board. In this latter case, the product ejectors project outwardly through the opening and above the outer surface of the die board. In both cases, the height of the product ejector is limited. It is recognized that the shorter the height of the product ejector, the more challenging it is to control or limit the pressure exerted by the product ejector against the die cut product. Also, there are limitations on the material options for product ejectors. As a practical matter, materials selected for use as product ejectors are materials that have been tried and used and which perform reliably over time in typical die cutting operations.
Thus, there is a need to develop a rotary cutting die cutting corrugated board that addresses the general problem of flute crushing.